I DON'T EXPECT to see any fish that large, but on our second day, with Hurricane Gustav churning its way up through the Caribbean toward the Gulf, it's my turn to go looking. We tie up to a platform and I jump into the 80-degree water.

Diving the rig is like swimming through the skeleton of a skyscraper: Fish weave through a lattice of support beams that drop ominously into infinity. Every inch of this maze of metal is covered with a spectrum of life. My urge to breathe is suppressed by fascination at the improbable wonder around me, and all I want to do is swim deeper and stay longer. At around 25 feet I pass through the murk layer and into 50 feet of visibility, like a plane rising out of the clouds and into clear skies.

The alarm that signals 30 feet comes not from my dive watch but from my ears. While taking the freediving course in Monterey, due to an old case of surfer's ear, I picked up an infection that has rendered me temporarily deaf in my left ear. At three stories down, it feels like there's a swollen balloon in my ear canal pressing against my skull. The malady is frustrating, because I won't be able to dive deep.

The water is thick with fish, but for these men the biomass is white noise to be filtered in search of real prizes. Head and Kirkconnell grab on to a crossbeam at 45 feet and hang in the current, a technique to conserve energy while waiting for fish. A cobia—a long, broad fish that resembles a shark—swims just out of range. Kirkconnell uses his prolific communication skills, which seem to transcend both species and mediums, by gulping out a grouper call to attract the curious cobia. The fish turns toward the men, who kick off the beam in its direction. Seconds later the hollow metallic pop of Head's gun signals the successful end of the hunt.

After geeking out on a colony of orange sponges on a crossbeam, I turn for the surface and nearly plow headfirst into a barnacle-encrusted beam. It could've knocked me out cold, and when I tell Kirkconnell about it, he says, "Welcome to the game."

We dive a couple more platforms and then pull anchor to head home as a stiff breeze washes over the bow. "There's the wind," says Clasen. "More of that coming."

Back at Venice Marina, near Pilottown, the few remaining people are loading their boats to tow inland. Homeowners board up windows, and New Orleans, 85 miles upriver, is already emptying. The guys have more immediate concerns. They have fish to clean.